It concerns the use of a specific electrical supply network associated with the presence of the recuperative braking system, and its object is an electrical supply system which is particularly well suited to equipment, the functioning of which generates large requirements for current over short periods of time, and the electrical supply of which must be provided within short response times, so as to permit dynamic functioning of the said equipment. Its object is also a micro-hybrid system which is designed for implementation of this system.
By way of example, in a vehicle, the equipment of this type which requires an electrical supply with short response times comprises in particular:                the so-called “e-turbo” electrically assisted turbo-compressor, or the so-called “e-charger” supercharger, this equipment typically requiring electrical power levels of 1 to 2 kW for a duration of 1 to 2 s. These power levels and durations can be higher, but without exceeding 3 kW and 3 s respectively. The response time of the supply must generally be less than a few tens of milliseconds;        the electric assisted steering, which in transitory conditions consumes current of between 25 and 100 A for durations of 1 to 2 ms;        the electric pump unit, which may require a current of approximately 100 A for a duration of approximately 200 ms; and        the electro-magnetically controlled valves which may require a current of approximately 40 A for a duration of 1 to 140 ms.        
The conventional electrical supply network of a motor vehicle usually comprises two sources of current, i.e. the battery (commonly a lead battery), and the alternator. However, these sources are both badly suited to supply with short response times to electrical equipment which can moreover generate strong demands for current or voltage.
In fact, the response time of a conventional alternator, of approximately a hundred milliseconds, is too lengthy to fulfil a need of this type.
The lead battery is also badly suited to cyclical supply, with short response times, of high current peaks, particularly because the discharge cycles which are then imposed on it contribute towards accelerating its ageing. Other types of battery could fulfil this need, but they are too costly to be able to envisage putting them into place on a mass-produced motor vehicle.
According to a first one of its characteristics, in vehicles which are equipped with micro-hybrid systems which can function in recuperative braking mode, the invention proposes the use of a specific electrical supply network associated with this functioning mode, in order to supply, with short response times, equipment of the vehicle which can moreover generate relatively large current requirements in dynamic functioning.
In a known manner, micro-hybrid systems, for example with an alternator-starter, make it possible to reduce the fuel consumption of a vehicle, and can function in recuperative braking mode. These systems generally comprise a reversible rotary electric machine, a reversible AC/DC converter, an auxiliary energy storage unit, and a reversible DC/DC converter, as well as a device for electronic control of the assembly. Preferably, the auxiliary energy storage unit consists of the association of a plurality of elementary capacitive cells with a very large capacity, which are also known as “super-capacitors”. The auxiliary energy storage unit and the reversible DC/DC converter form the “power pack” of the micro-hybrid system.
Also in a known manner, the electrical energy which is recuperated by means of the rotary electric machine, for example when the assembly is functioning in recuperative braking mode, is stored in the auxiliary energy storage unit. The micro-hybrid system with recuperative braking provides a dual voltage network which is capable of providing firstly a direct floating voltage which is obtained at the terminals of the auxiliary energy storage unit, and secondly a low direct voltage at the terminals of the lead battery. The floating direct voltage which is known as “14+X voltage” is higher than the voltage at the terminals of the said lead battery which supplies the 12V electrical supply network in a conventional manner.
The capacitive elements of the auxiliary energy storage unit make it possible to supply high current during short periods, and also make possible the supply of current with a very short response time, which is compatible with the supply to specific electrical equipment of the vehicle.